What causes chickenpox?

The main symptom of chickenpox is an itchy rash that quickly turns into fluid-filled blisters and then to scabs that fall off as the infection fades.

When the blisters pop, often due to scratching because they are so itchy, the virus is released into the surroundings as tiny droplets. The infection spreads easily through sneezing and coughing, and by direct contact with an infected person or with something they've touched (NHS 2016a, PHE 2015).

Chickenpox is considered to be contagious for a couple of days before the rash shows (PHE 2015), but is actually most infectious once the rash appears. From then on, a person is infectious for between five and six days, at which point the spots should dry and crust over (Harding 2016, NHS 2016a, RCOG 2015a).

Will it harm my unborn baby if I catch chickenpox?

It can be dangerous for you and your baby if you’ve never had chickenpox and you catch it during pregnancy.

But this is very unlikely to happen, because chickenpox was a common childhood illness before varicella was added to the Childhood Immunisation Schedule in 2005. So if you grew up in Australia, it’s most likely you’ve had it as a child. This is the case for more than 90 per cent of pregnant women in Australia (Gilbert 2002).

Once you’ve had chickenpox or been immunised against it, your body makes antibodies to the virus. This means you’re immune and extremely unlikely to ever get it again (RCOG 2015b).

Chickenpox is much less common in tropical countries. If you grew up in one of these countries, it's less likely that you had it as a child. Therefore, you're less likely to have the protection of immunity (Rice 2011).

The few women who do catch chickenpox during pregnancy are always referred to a fetal medicine specialist for extra care and monitoring.

Most of these women and their babies remain well despite the infection (NHS 2016b). There’s no evidence that you’re more likely to have a miscarriage if you develop chickenpox in your first trimester (RCOG 2015a).

But there’s a small possibility that chickenpox could cause an unborn baby to develop a condition called fetal varicella syndrome (FVS).

Babies with FVS are born with serious abnormalities such as scars, shortened limbs, and eye, brain, bowel and bladder problems. They can also have learning difficulties (HPA 2011, Sinha et al 2012).

The risks of FVS depend on when during your pregnancy you get chickenpox:

Before 28 weeks in the womb (uterus), the risk that your baby develops FVS is small.

After 28 weeks, your baby is unlikely to be affected by FVS. But he may develop shingles in his first few years of life.

(RCOG 2015a, b)

After you’ve recovered from chickenpox, your doctor will refer you for a detailed ultrasound scan, to check how your baby is doing (Harding 2016, Shrim et al 2012).

This will look at your baby more carefully than a normal scan, to check that his limbs and internal organs are healthy (RCOG 2015a). You may need more than one detailed scan to monitor your baby's wellbeing.

If you develop chickenpox within seven days before or after giving birth, your baby may also go on to have severe chickenpox. In a newborn baby, chickenpox can cause severe or, rarely, life-threatening illness (NHS 2016a, PHE 2015).

Chickenpox during pregnancy can be harmful for mums-to-be as well as their babies. Chickenpox can sometimes lead to serious complications. These complications could make you extremely ill. For example, about one in 20 pregnant women with chickenpox develops pneumonia (NHS 2016a).

If you're a smoker, your doctor will strongly advise you to quit. As well as the usual risks to your baby posed by smoking, it will greatly increase your risk of getting chickenpox pneumonia, which can be fatal (Mohsen and McKendrick 2003, PHE 2015).

It's very important to tell your doctor straight away if you have a rash of any kind during pregnancy. In addition to chickenpox, there are several medical conditions that cause a rash, and some can affect your unborn baby or make you very ill (MacMahon 2012).

Even if you don’t have a rash yet, tell your doctor or midwife if you've been exposed and you’ve never had chickenpox before. If you're not sure, it’s safest to talk to her.

I don’t know if I’ve had chickenpox. What should I do?

If you haven't had a varicella vaccination and think you’ve been exposed to the varicella virus, but you’re unsure whether or not you’ve had chickenpox before, see your doctor or midwife straight away (NHS 2015a).

Your doctor will offer to take a blood test to check for chickenpox antibodies (RCOG 2015b). The test result will show whether you've had chickenpox as a child.

If you are exposed to the virus, even if you think you may be immune, talk to your doctor or midwife, as you should be tested for immunity (PHE 2015).

Unfortunately, if you’re found to be non-immune to chickenpox, you can't be vaccinated during pregnancy because it could harm your unborn baby (ATAGI 2013, RCOG 2015b). You'll have to wait until after your baby is born to be vaccinated (PHE 2015, RCOG 2015b).

It's always best to be cautious, and avoid contact with anyone who may have the virus. Chickenpox spreads easily enough that you can pick it up if you're in the same room with someone who has it (Fox et al 2010, PHE 2015, RCOG 2015b).

You can also catch chickenpox from someone who has shingles, because it’s caused by the same virus (NHS 2016a, NSWH 2014).

How will I be treated if I’m exposed to chickenpox in pregnancy?

If you’re found to be non-immune to chickenpox and you’ve been exposed to the virus, your doctor will recommend that you have an injection of VZIG (ASID 2014, RCOG 2015b). VZIG stands for varicella-zoster immune globulin (VZIG). It’s a blood product that contains antibodies against the virus (PHE 2015).

VZIG won’t help you or your baby if you’ve already developed the chickenpox rash (RCOG 2015b). It only works if you have it before you develop symptoms. This means it needs to be given as soon as possible after any exposure to the virus.

Given at the right time, VZIG can make chickenpox much milder and last for a shorter time (RCOG 2015b). There is also evidence that VZIG may protect your baby from catching the virus in the womb.

Ideally, you should have the VZIG injection within 72 hours of exposure to chickenpox, or at the very latest within 10 days, for it to work (ASID 2014, Cohen et al 2011, RCOG 2015b).

If you develop a rash despite having VZIG, your doctor may offer you an anti-viral drug called acyclovir (ASID 2014, UKTIS 2015). This will reduce your fever and other symptoms, and may make the rash milder. Acycolvir has a good safety record in pregnancy (UKTIS 2015).

Treatment with acyclovir should happen as soon as possible after chickenpox symptoms have appeared, ideally within 24 to 48 hours (NICE 2016). If you smoke and develop chickenpox, it’s even more important that you discuss taking acyclovir with your doctor. Your risks of becoming very ill with pneumonia are much more serious if you smoke (PHE 2015).

It’s safe to take paracetamol to treat any fever you may have (NHS 2015b). You can use calamine lotion to reduce the itchiness of your spots (NICE 2016).

How is chickenpox treated in newborns?

If you have chickenpox around the time your baby is born, a doctor will give your baby an injection of VZIG to try to prevent him from getting chickenpox (ASID 2014, PHE 2015).

Even so, about half of newborns whose mums have chickenpox and who have VZIG still develop chickenpox, although the symptoms may be less severe. If your baby develops chickenpox within seven days of being born, your doctor will recommend treatment with acyclovir (PHE 2015).

If you’re a mum with chickenpox, be reassured that you can still breastfeed your new baby if you want to and feel up to it, as long as you don’t have any blisters near your nipples (ASID 2014, ATAGI 2013, RCOG 2015a).

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